1. Field of the Invention
The present invention relates to a relay apparatus for relaying transmission among a plurality of wireless terminals in a coverage area of the relay apparatus with a limited bandwidth, like an access point in a wireless LAN (local area network).
2. Description of Related Art
Recently, for example, as in an IP telephone via a wireless LAN, a wireless terminal that performs a telephone conversion via radio transmission has become widespread. The wireless terminal that performs a telephone call via radio transmission enables a telephone call with a terminal on a partner side by performing radio transmission with a relay apparatus (e.g., an access point of a wireless LAN, etc.). In such a transmission form, mobile terminals are present in a coverage area of a relay apparatus, whereby simultaneous telephone calls by the mobile terminals occur. In this case, those mobile terminals share a transmission bandwidth available in the relay apparatus, and perform transmission respectively. Therefore, when the number of mobile terminals that perform telephone calls simultaneously via one relay apparatus increases, the transmission bandwidth becomes insufficient. Consequently, at a mobile terminal, delays in voice data transmission from a terminal on a partner side are increased, and a noise such as a sound break occurs. This problem may occur in the case of communicating data such as music or a moving picture by streaming, as well as in the case of a telephone call.
As a method for preventing the shortage of a transmission bandwidth in a relay apparatus, for example, the following method has been proposed: in a system for distributing a time-varying image to a wireless terminal via a relay apparatus from an image transmission apparatus, a part of an image frame contained in the time-varying image to be distributed to the wireless terminal is discarded when the transmission condition in a wireless zone between the relay apparatus and the wireless terminal degrades (e.g., see JP 2003-87170 A).